Performance and storage life of rain repellents

ABSTRACT

An alcohol and water solution of a silicone polymer consisting of an acid neutralized cationic polysiloxane copolymer containing amino functional groups is heated in an enclosed aluminum container to form a barrier coating inside the container and to enhance the performance characteristics of the polymer in imparting visibility through a transparent surface during water impingement.

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[54] PIERIFURMANCE AND STORAGE LHlFlE 3,460,981 8/1969 Keil et al..l06/13 X @11 HAHN REPELLENTS 3,516,854 6/1970 Curry ..ll7/l35.5 X

[72] lnventor: David W. Clarke, Rcnton, Wash. Primary Examiner Lorenzo BHayes [73] Assignee: The Boeing Company, Seattle, Wash. Attorney-GlennOrlob and Kenneth W. Thomas [22] Filed: June 15, 1970 An alcohol andwater solution of a silicone polymer consisting [52] 1 23 2 of an acidneutralized cationic polysiloxane copolymer con- [51] lint. Cl. .C09k3/1l 8 mining amino functional gmups is heated in an enclosed 53 1mmnewt-e11 ..l06/2, 13, 287 c-,117/135.1, mimlm miner a barrier coatinginside the 117/ 35 5 tainer and to enhance the performancecharacteristics of the polymer in imparting visibility through atransparent surface [56] Refielrences Cited during water impingement.

UNITED STATES PATENTS 4 Claims, No Drawings 2,991,204 7/1961 Astle..l48/6.27 X

PERFORMANCE AND STORAGE lLlFE 01F RAIN REPELLENTS Rain repellents arefinding widespread use on vehicles wherein the repellent is applied tothe surface of the windshield to form a hydrophobic film. The film istransparent, it prevents rain from building up on the surface, andthereby maintains excellent visibility through the windshield even in aheavy rainstorm. The repellent should have a storage life of severalmonths without losing its effectiveness when placed in use.

Rain repellents of an acid neutralized cationic dimethyl polysilox'anepolymer containing amino functional groups are among the best of therain repellents. These repellents in lower alcohol-water solutions maybe stored in stainless steel, in glass, or in inert plastic containersand have a good storage life. These diluted repellents could not bestored in aluminum containers prior to this invention as the copolymerreacts with the aluminum and thereby loses its effectiveness in a matterof days.

For marketing and usage advantages, it is often desirable to store therepellent in pressurized aluminum aerosol containers, therefore,attempts were made to line the containers to form a barrier which willprevent interaction with the aluminum and the repellent. Several organicand organosilicon linings were introduced into aluminum aerosolcontainers. Even the best of these coatings prevented the metal andrepellent from interacting for no more than several weeks. A sulfuricacid anodized coating applied to the interior of aluminum containersgave only a limited storage life when used as a container for these rainrepellents. it is known that a corrosion resistant film can be impartedto the inside of aluminum containers by placing about a 0.01 to 0.1normal solution of triethanolamine or of ammonium hydroxide inside thecontainers and heating from about 98 to 160 C. (208320 F.) for minuteswith maximum corrosion protection obtained after 4 hours. Aluminumaerosol containers were treated thus with triethanolamine, with ammoniumhydroxide and with various other dilute solutions of other lower amines.Rain repellents stored in containers so treated were degraded afterabout a month of storage.

None of the usual methods of coating an aluminum container to render itcorrosion resistant are effective in preventing interaction between therain repellent and the container. It appears that all of the coatingsare porous.

It was discovered that a dense, nonporous, barrier coating can beobtained by heating the water alcohol solution of rain repellent in theenclosed aluminum container. The repellent may then be stored in thesame container; it has a good storage life and the performancecharacteristics are enhanced. The container with repellent is heated fora time sufficient to build a coating on the inside of the container. Thelength of time at temperature varies with the temperature. Slightlyelevated temperatures require considerable time at temperature. Athigher temperatures the coating is obtained in a shorter period. Aneffective coating may be built up and repellency performancecharacteristics enhanced by heating at 130 F. for 3 months, by heatingat 160 F. for 5 days, by heating at 300 F. for 30 minutes and by heatingat various temperatures and times between these figures.

An object of this invention is to obtain adequate storage life for anacid neutralized cationic polysiloxane polymer containing aminofunctional groups when diluted in water-alcohol solutions and stored inan aluminum container.

Another object is to impart improved performance characteristics to apolysiloxane rain repellent.

Yet another object is to coat the inside of an aluminum container toobtain a pinhole-free impervious coating.

An acid neutralized cationic dimethyl polysiloxane polymer containingamino functional groups when diluted in a mixture of lower alcohol andwater and stored in an enclosed aluminum container at room temperaturefor a few days loses its effectiveness as a material for retainingtransparency through a transparent material subjected to waterimpingement. The container remains bright and shiny. When the solutionand container are heated to a temperature of about 130 F. to 300 F. andare held at the elevated temperature for sufficient time, a dull graycoat is built up in the container in both the liquid and the vaporphase. This treatment is also effective in aluminum containers having astainless steel valve assembly. The coat formed is dense and pinholefree. It shows a resistance of over a million ohms when tested by a DCohmmeter. It prevents interaction between the polymer and the aluminumto give storage life of 2 years or more to the repellent fluid whenstored in the treated aluminum container.

At the same time that the coating is being formed a change is takingplace in the copolymer such that its effective film life is lengthenedwhen applied to a transparent surface. The same change to the copolymertakes place when the water-alcohol diluted polymer is heated in glass,in stainless steel or in an inert plastic container such as polyethyleneto which aluminum particles have been added. its performance is notenhanced by heating in these containers unless aluminum is present.

EXAMPLE 1 A rain-repellent fluid comprising 84 weight percent distilledwater, 14 weight percent isopropanol (99 percent) and 2 weight percentof the following composition: 43.0 parts (by weight) of a hydroxylatedpolydimethylsiloxane having an average molecular weight of about 2,000;4.2 parts, (by weight) of n-(dimethoxymethylsilylisobutyl) ethylenediamine; 3.0 parts (by weight) of glacial acetic acid; and 49.8 parts(by weight) of tertiary butanol was placed in a seamless aerosol can ofANS (American National Standards) H35.l1969, 1100 series alloy aluminumhaving a AlSl (American Iron and Steel Institute), 300 series stainlesssteel valve. The cans were treated by heating at various temperaturesthen cooled to ambient temperature. The treated fluid was then appliedto a section of glass which was being subjected to simulated rainfall atl.4 inches per hour, driven by a stream of air at about 100 knots. Theglass was inclined at 45 to the direction of the flow of air. Visibilityperformance was as shown in table 1. It illustrates the effectiveness ofthe heat treating process in imparting shelf life and in enhancing theperformance characteristics of the fluid.

Visibility performance is determined by looking through an inclinedtransparent member toward impinging water. By looking toward a target inthe background, the observer can judge the degree of visibility providedby the rain repellent fluid applied to the transparent member. For goodvisibility the water does not wet the window, but balls up in smalldroplets which are blown off by the moving air stream. This allows theeye to see between the drops and integrate in a manner similar tolooking through a woven window screen. As the effectiveness of therepellent gradually decreases the size of the water drops on the surfaceincrease, the drops grow tails to resemble polliwogs, then the dropsgrow longer until at about 2 inches long they are termed smallrivulets." In time the "small rivulets become large rivulets whicheventually merge to form small stationary wettable spots of one-quarterinch or more in diameter. During this period visibility deterioratesfrom excellent" to good" to fair."

By looking at the water fonnations racing off the window, instead oflooking through at the target, the observer can estimate rather closelythe rate at which the rain-repellent film is deteriorating, and canregister the time from initial application until polliwogs or rivulets,"or wettable spots form.

EXAMPLE 2 Rain-repellent fluid was prepared, placed in an aluminumcontainer and heat treated, all as in example 1. Observations were madeas to film life performance of the rain repellent. Results of theobservations are shown in table 2. All observations were discontinuedafter 30 minutes. Therefore, all tests showing 30 minutes were actually30 minutes or more. N.A. indicated the information is not available.This table illustrates the increase in performance as a result of heattreatment.

TABLE 2 Time required to reach condition (min) Wet- Time in 1" polli-Small table Heat treatment storage wogs rivulets spots None Nne NA 7 20hour at 225 F -do 8 28 2hours at 225 F do NA 10 26 5 hours at 225 F- do10 13 30 10 hours at 225 F 27 30. hour at 300 F 5 10 26 1hr. at 300152... NA 10 30 2 hours at 300 F 15 Z) 30 None Zero NA NA 5 hours at 225F 12 NA NA 2 hours at 300 F 18 NA NA, None 5 10 18 5 hours at 225 F 6 15NA 2 hours at 300 F do 5 15 NA EXAMPLE 3 A rain-repellent fluidcomprising 84 weight percent distilled water, 14 weight percentisopropanol (99 percent) and 2 weight percent of the followingcomposition: 43.0 parts (by weight) of a hydroxylatedpolydimethylsiloxane having an average molecular weight of about 1,000;4.2 parts (by weight) of glacial acetic acid; and 49.8 parts (by weight)of tertiary butanol was placed in a seamless aerosol can of ANS 1000series aluminum allot having an MS] 300 series stainless steel valve.The can containing the repellent solution was heated at 250 F. for 5hours and placed in storage 5 months then tested in the equipment asoutlined in example 2. Small rivulets formed in 5 minutes and smallwettable areas formed in 17 minutes.

I claim:

1. A method of treating an enclosed aluminum container to form apinhole-free coating on the inside of the container with the stepscomprising;

a. introducing a water-repellent fluid comprising about 2 weight percentof an acetic acid neutralized copolymer of a hydroxylatedpolydimethylsiloxane with an average molecular weight of about 2,000 andn-(dimethoxymethylsilylisobutyl) ethylene diamine in a water and alcoholsolution wherein the alcohol is selected from the group consisting ofisopropanol and tertiary butanol, and

b. heating the repellent and the enclosed aluminum container to atemperature of from about l60 to 300 F. for a time at temperaturesufiicient to build a coating inside the container.

2. A method as in claim 1 wherein the repellent and container is heatedto a temperature of about 300 F. for 30 minutes to 2 hours.

3. A method of increasing effective film life of a rain repellent whenbeing used to impart visibility through a transparent member duringwater impingement on the member, with the repellent comprising; a waterand alcohol solution of an acid neutralized cationic dimethylpolysiloxane polymer containing amino functional groups in thepercentages of 84 weight percent water, 14 weight percent isopropanol(99percent) and 2 weight percent 0 the following composition: 43 parts,by

weight, of a hydroxylated polydimethylsiloxane having an averagemolecular weight of about 2,000; 4.2 parts, by weight, ofn-(dimethoxymethylsilylisobutyl) ethylene diamine; 3 parts, by weight,of glacial acetic acid; and 49.8 parts, by weight, of tertiary butanol,the steps comprising; placing the repellent solution into an enclosedaluminum container, and heating the repellent while in the container toa temperature of from about to 300 F. for a time sufficient to build acoating inside the container.

4. A method as in claim 3 wherein the repellent and enclosed aluminumcontainer is heated to a temperature of about 300 F. for 30 minutes to 2hours.

2. A method as in claim 1 wherein the repellent and container is heatedto a temperature of about 300* F. for 30 minutes to 2 hours.
 3. A methodof increasing effective film life of a rain repellent when being used toimpart visibility through a transparent member during water impingementon the Member, with the repellent comprising; a water and alcoholsolution of an acid neutralized cationic dimethyl polysiloxane polymercontaining amino functional groups in the percentages of 84 weightpercent water, 14 weight percent isopropanol (99percent) and 2 weightpercent of the following composition: 43 parts, by weight, of ahydroxylated polydimethylsiloxane having an average molecular weight ofabout 2,000; 4.2 parts, by weight, of n-(dimethoxymethylsilylisobutyl)ethylene diamine; 3 parts, by weight, of glacial acetic acid; and 49.8parts, by weight, of tertiary butanol, the steps comprising; placing therepellent solution into an enclosed aluminum container, and heating therepellent while in the container to a temperature of from about 160* to300* F. for a time sufficient to build a coating inside the container.4. A method as in claim 3 wherein the repellent and enclosed aluminumcontainer is heated to a temperature of about 300* F. for 30 minutes to2 hours.